Wound healing is a complex process involving multiple cell types, but invasion of nearby fibroblasts into the clot is considered the rate-limiting step. The rate of fibroblast invasion is in turn controlled, to a significant extent, by the action of platelet-derived growth factor (PDGF) released by platelets and macrophages in the clot. The basis of this proposal is to explore the prospect that mathematical modeling can be used to bridge the fundamental gap between in vitro studies of cell signaling at the molecular/cellular levels, performed under controlled experimental conditions, and physiological settings where cell population behaviors evolve dynamically. In general, targeted molecular therapeutic strategies will have the most benefit if they are informed by molecular-, cellular-, and tissue-level design principles. Based on indications from previous and preliminary work, we have formulated a new, hypothetical model with the potential for redefining the mechanisms by which migration of fibroblasts and similar cell types is spatially directed. We aim to explore this and alternative models in quantitative terms through a combination of experimental and computational approaches. Intracellular signaling through the PI 3-kinase pathway will be monitored in living fibroblasts, using total internal reflection fluorescence (TIRF) microscopy, as the cells sense and respond to PDGF gradients. In these experiments, morphological polarity and cell migration will also be tracked, in an effort to quantitatively relate migration speed and turning behavior to the pattern of PI 3-kinase activation. Preliminary work has shown that cell polarity imposes an intrinsic bias in PI 3-kinase signaling, which is reinforced by PDGF when cells migrate up-gradient. To further test this mechanism, cell polarity will be disrupted using a variety of molecular perturbations, and the effects on PI 3-kinase signaling will be analyzed. Finally, the relationships among PI 3-kinase signaling, cell polarity, and cell migration will be incorporated in a biased random walk model, which will ultimately define the cell flux term in a model of fibroblast invasion. These efforts will serve as a foundation for more in-depth studies of molecular mechanisms governing physiological processes. [unreadable] [unreadable] [unreadable]